Last week, the U.K. House of Commons voted to legalize a controversial in vitro fertilization technique called mitochondrial donation, popularly known as the “three-parent baby” technique. The technique is intended for mothers who have an inherited genetic defect in their mitochondria - the fuel compartments that power our cells - and can help them from passing on the incurable disease that often entails years of suffering and ends in premature death.

Doctors replace the DNA from a donor egg with the mother’s DNA, use sperm from the father to fertilize it, then implant it into the mother’s uterus via IVF technology. The donor egg’s cytoplasm contains defect-free mitochondria and DNA from both parents. Proponents say the technique gives parents with mitochondrial disease the chance to have disease-free children, but critics say it brings us one step closer to the reality of genetically modified "designer babies."

On Friday, Stanford law professor and biotechnology ethicist Hank Greely, JD, was among the guests on KQED’s Forum broadcast to discuss the issue. He’s in favor of the procedure, noting that when looking at genetic modifications, "the purpose, the nature, [and] the safety" should be considered. "There are some things that I think shouldn’t be done," he said, adding that "things like this, which gives women who have defective mitochondrial DNA their only chance to have genetic children of their own... if the safety proves up... seems to be a good use."

The scenario many of us learned in school is that two X chromosomes make someone female, and an X and a Y chromosome make someone male. These are simplistic ways of thinking about what is scientifically very complex.